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Japan's space agency has finalized a plan to send a probe to the Martian moons of Phobos and Deimos, and it includes an ambitious lander to collect samples from Phobos to return to Earth.

The agency, JAXA, submitted the plan to the country's science ministry on Wednesday, the Asahi Shimbun newspaper reported. On Twitter, the Martian Moons Exploration (MMX) official account also announced that it had formally moved from design into the "development" phase of operations. The space agency estimated that the total cost for the mission would come to $417 million.

The current plan calls for a 2024 launch of the probe on an H-3 rocket, a new booster built by Mitsubishi Heavy Industries and expected to debut late this year or in 2021. The MMX spacecraft would enter into orbit around Mars in 2025 and return to Earth in 2029.

Japan has experience with similar kinds of missions to small bodies in the Solar System. Its Hayabusa-2 probe successfully grabbed material from surface of the asteroid Ryugu and is scheduled to return the asteroid samples to Earth late this year. With a diameter of just 23km, Phobos has a surface gravity that is about one-thousandth that of Earth.

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The MMX team has already said it plans to work on a similar small lander to Hayabusa-2 for the Mars mission, collaborating with the German and French space agencies.

No spacecraft have yet flown to Mars with the designated purpose of studying its small moons, nor has material ever been collected from them. Scientists would be keen to study the surface of a moon other than that of Earth's companion, which should help them better understand the formation of terrestrial planets. For Phobos and Deimos, it is also important to understand whether they are captured asteroids or fragments of the red planet ejected during some ancient impact.

Detailing the surface of Phobos is also important because it's possible that the first human missions to Mars will land there rather than on the surface of Mars. With its much smaller gravity well, it would be much easier for astronauts to leave Phobos for the return journey to Earth than the surface of Mars itself.

An odd thought struck me while reading the article. From other space articles, I’ve learned that any launch from a planetary body that doesn’t escape the planetary orbit still has its periapsis intersecting with the planetary surface, where it originally departed from. A circularisation burn is required to lift the periapsis so that a full orbit is possible. What sort of orbital mechanics would permit ejecta from a planetary collision to enter orbit? How can the orbit be circularised, so that it neither escapes nor re-collides?

Detailing the surface of Phobos is also important because it is possible that the first human missions to Mars will land there, rather than on the surface of Mars. With its much smaller gravity well, it would be much easier for astronauts to leave Phobos for the return journey to Earth than the surface of Mars itself.

How much total delta-V does this actually save? You would save ~ 5 km/s from not having to lift of Mars surface; but you'd also be taking a penalty on arrival for entering orbit. Doing so requires more delta-V than landing because you can shed a large fraction of your velocity via aerobraking if you go for a landing.

Detailing the surface of Phobos is also important because it is possible that the first human missions to Mars will land there,

Landing is something of a misnomer. With an escape velocity of around 11m/s (41km/h) - Phobos is sufficiently aspheric that it doesn't have a constant surface gravity - any rendezvous would be more like docking than an actual landing. You'd approach at a crawl and then secure yourself with tethers. (Hopefully the harpoons will work better the second time around.)

Detailing the surface of Phobos is also important because it is possible that the first human missions to Mars will land there, rather than on the surface of Mars. With its much smaller gravity well, it would be much easier for astronauts to leave Phobos for the return journey to Earth than the surface of Mars itself.

How much total delta-V does this actually save? You would save ~ 5 km/s from not having to lift of Mars surface; but you'd also be taking a penalty on arrival for entering orbit. Doing so requires more delta-V than landing because you can shed a large fraction of your velocity via aerobraking if you go for a landing.

I think you can still use aerobraking to enter orbit around Mars, though it takes longer since you typically will slow down in smaller increments. I think MAVEN has used aerobraking extensively to enter and alter its orbit around Mars.

An odd thought struck me while reading the article. From other space articles, I’ve learned that any launch from a planetary body that doesn’t escape the planetary orbit still has its periapsis intersecting with the planetary surface, where it originally departed from. A circularisation burn is required to lift the periapsis so that a full orbit is possible. What sort of orbital mechanics would permit ejecta from a planetary collision to enter orbit? How can the orbit be circularised, so that it neither escapes nor re-collides?

Our moon formed in-place from a cloud of debris that was knocked into orbit. Not all particles take exactly the same trajectory. They bounce off each other which resulted in some coming back to earth faster and some staying in orbit. Once there, gravitational attracting creates more collisions to scrub relative velocities until everything was close enough together to form a solid body.

Detailing the surface of Phobos is also important because it is possible that the first human missions to Mars will land there, rather than on the surface of Mars. With its much smaller gravity well, it would be much easier for astronauts to leave Phobos for the return journey to Earth than the surface of Mars itself.

How much total delta-V does this actually save? You would save ~ 5 km/s from not having to lift of Mars surface; but you'd also be taking a penalty on arrival for entering orbit. Doing so requires more delta-V than landing because you can shed a large fraction of your velocity via aerobraking if you go for a landing.

You can do a Mars aerobrake maneuver to shed most of the interplanetary velocity, pop out of the atmosphere, and then do a burn to raise your orbit so it stays out of the atmosphere, and then proceed on to Phobos. Whether that's easier from an engineering/flight-planning/cost perspective than "simply" upping the mass budget for fuel is probably not a simple question to answer.

Detailing the surface of Phobos is also important because it is possible that the first human missions to Mars will land there, rather than on the surface of Mars. With its much smaller gravity well, it would be much easier for astronauts to leave Phobos for the return journey to Earth than the surface of Mars itself.

How much total delta-V does this actually save? You would save ~ 5 km/s from not having to lift of Mars surface; but you'd also be taking a penalty on arrival for entering orbit. Doing so requires more delta-V than landing because you can shed a large fraction of your velocity via aerobraking if you go for a landing.

I think you can still use aerobraking to enter orbit around Mars, though it takes longer since you typically will slow down in smaller increments. I think MAVEN has used aerobraking extensively to enter and alter its orbit around Mars.

The aerobraking maneuver that puts things in orbit typically on uses that to circularize from a long elliptical orbit - not enough to scrub all of the trans-orbital speed. That process takes months. A SpaceX-style aero maneuver will be a single pass.

Detailing the surface of Phobos is also important because it is possible that the first human missions to Mars will land there, rather than on the surface of Mars. With its much smaller gravity well, it would be much easier for astronauts to leave Phobos for the return journey to Earth than the surface of Mars itself.

How much total delta-V does this actually save? You would save ~ 5 km/s from not having to lift of Mars surface; but you'd also be taking a penalty on arrival for entering orbit. Doing so requires more delta-V than landing because you can shed a large fraction of your velocity via aerobraking if you go for a landing.

You can do a Mars aerobrake maneuver to shed most of the interplanetary velocity, pop out of the atmosphere, and then do a burn to raise your orbit so it stays out of the atmosphere, and then proceed on to Phobos. Whether that's easier from an engineering/flight-planning/cost perspective than "simply" upping the mass budget for fuel is probably not a simple question to answer.

It's not something we've ever done. It's theoretically possible. Aerobraking is "easy" when you're targeting zero velocity. It's also easy when you brush the top of the atmosphere over the period of several passes. To do what you're suggesting would require threading the needle in a single pass that scrubs just the right amount of energy.

Japan might be starting a nice little niche of these trips to non planets and bringing stuff back.

Long term it could make sense economically.

It might be feasible economically to use space resources for space structures in this century, but bringing it back to Earth would require a huge breakthrough in space launch tech. A few orders of magnitude in cost reductions is necessary.

Detailing the surface of Phobos is also important because it is possible that the first human missions to Mars will land there, rather than on the surface of Mars. With its much smaller gravity well, it would be much easier for astronauts to leave Phobos for the return journey to Earth than the surface of Mars itself.

How much total delta-V does this actually save? You would save ~ 5 km/s from not having to lift of Mars surface; but you'd also be taking a penalty on arrival for entering orbit. Doing so requires more delta-V than landing because you can shed a large fraction of your velocity via aerobraking if you go for a landing.

You can do a Mars aerobrake maneuver to shed most of the interplanetary velocity, pop out of the atmosphere, and then do a burn to raise your orbit so it stays out of the atmosphere, and then proceed on to Phobos. Whether that's easier from an engineering/flight-planning/cost perspective than "simply" upping the mass budget for fuel is probably not a simple question to answer.

It's not something we've ever done. It's theoretically possible. Aerobraking is "easy" when you're targeting zero velocity. It's also easy when you brush the top of the atmosphere over the period of several passes. To do what you're suggesting would require threading the needle in a single pass that scrubs just the right amount of energy.

They could plan to do two passes. One pass to remove 95% to 99% of the energy you need to shed, or whatever accuracy range is believed achievable, then a second pass to remove the rest. Or three passes, if that's what's required. They could have a Mars probe try this, to prove out the concept.

Detailing the surface of Phobos is also important because it is possible that the first human missions to Mars will land there, rather than on the surface of Mars. With its much smaller gravity well, it would be much easier for astronauts to leave Phobos for the return journey to Earth than the surface of Mars itself.

How much total delta-V does this actually save? You would save ~ 5 km/s from not having to lift of Mars surface; but you'd also be taking a penalty on arrival for entering orbit. Doing so requires more delta-V than landing because you can shed a large fraction of your velocity via aerobraking if you go for a landing.

You can do a Mars aerobrake maneuver to shed most of the interplanetary velocity, pop out of the atmosphere, and then do a burn to raise your orbit so it stays out of the atmosphere, and then proceed on to Phobos. Whether that's easier from an engineering/flight-planning/cost perspective than "simply" upping the mass budget for fuel is probably not a simple question to answer.

It's not something we've ever done. It's theoretically possible. Aerobraking is "easy" when you're targeting zero velocity. It's also easy when you brush the top of the atmosphere over the period of several passes. To do what you're suggesting would require threading the needle in a single pass that scrubs just the right amount of energy.

Yeah, I know. It was more of a hypothetical than anything else. Looking at insertion maneuvers for various Mars orbiters, the standard approach seems to be to do most of the job with thrusters and possibly to use repeated shallow aerobrakes to help in the final circularization. Here's Wikipedia describing the insertion of Mars Reconnaissance Orbiter:

Quote:

MRO began orbital insertion by approaching Mars on March 10, 2006, and passing above its southern hemisphere at an altitude of 370–400 kilometers (230–250 mi). All six of MRO's main engines burned for 27 minutes to slow the probe from 2,900 to 1,900 meters per second (9,500 to 6,200 ft/s). The helium pressurization tank was colder than expected, which reduced the pressure in the fuel tank by about 21 kilopascals (3.0 psi). The reduced pressure caused the engine thrust to be diminished by 2%, but MRO automatically compensated by extending the burn time by 33 seconds.[16]

Completion of the orbital insertion placed the orbiter in a highly elliptical polar orbit with a period of approximately 35.5 hours.[17] Shortly after insertion, the periapsis – the point in the orbit closest to Mars – was 426 km (265 mi) from the surface[17] (3,806 km (2,365 mi) from the planet's center). The apoapsis – the point in the orbit farthest from Mars – was 44,500 km (27,700 mi) from the surface (47,972 km (29,808 mi) from the planet's center).

On March 30, 2006, MRO began the process of aerobraking, a three-step procedure that cuts in half the fuel needed to achieve a lower, more circular orbit with a shorter period. First, during its first five orbits of the planet (one Earth week), MRO used its thrusters to drop the periapsis of its orbit into aerobraking altitude. This altitude depends on the thickness of the atmosphere because Martian atmospheric density changes with its seasons. Second, while using its thrusters to make minor corrections to its periapsis altitude, MRO maintained aerobraking altitude for 445 planetary orbits (about five Earth months) to reduce the apoapsis of the orbit to 450 kilometers (280 mi). This was done in such a way so as to not heat the spacecraft too much, but also dip enough into the atmosphere to slow the spacecraft down. After the process was complete, MRO used its thrusters to move its periapsis out of the edge of the Martian atmosphere on August 30, 2006.[18][19]

In September 2006 MRO fired its thrusters twice more to fine-tune its final, nearly circular orbit to approximately 250 to 316 km (155 to 196 mi) above the Martian surface, with a period of about 112 minutes.[20][21] The SHARAD radar antennas were deployed on September 16. All of the scientific instruments were tested and most were turned off prior to the solar conjunction that occurred from October 7 to November 6, 2006. After the conjunction ended the "primary science phase" began.

They could plan to do two passes. One pass to remove 95% to 99% of the energy you need to shed, or whatever accuracy range is believed achievable, then a second pass to remove the rest. Or three passes, if that's what's required. They could have a Mars probe try this, to prove out the concept.

You're on a hyperbolic trajectory. You only get one attempt. Once you successfully capture, then you can slowly adjust your orbit from there, but that first pass is the tough one.

Aerocapture is the process of using the atmosphere to capture from a hyperbolic to an elliptical orbit. Aerobraking is the process of reducing your apoapsis altitude using hundreds of drag passes. No one has tried aerocapture at Mars since that’s scary and would involve onboard processing to deal with the variability of Mars’ atmosphere. Aerobraking was performed by MGS, Odyssey, MRO, Maven (late in the mission) and ESAs TGO and is well established if a bit stressing on the ops teams.

They could plan to do two passes. One pass to remove 95% to 99% of the energy you need to shed, or whatever accuracy range is believed achievable, then a second pass to remove the rest. Or three passes, if that's what's required. They could have a Mars probe try this, to prove out the concept.

You're on a hyperbolic trajectory. You only get one attempt. Once you successfully capture, then you can slowly adjust your orbit from there, but that first pass is the tough one.

Right, but the point is you don't need to get right from your hyperbolic trajectory to one particular orbit. There's a range where you've shed enough momentum to be captured.